Hi Ben,
100% yes,
This is a typical appearance of perineal subluxation.
There would have been a palpable snap as the tendons transposed their positions and this commonly leads to tendinosis and eventual tenosynovitis.
There are two patterns I observe with peroneal tendon subluxation.
The first is where the superior peroneal retinaculum has been completely torn and the peroneal tendons migrate from behind the lateral malleolus to a position on top of the lateral malleolus. This is easy to feel clinically as you can feel the tendons snapping up and over the malleolus.It feels similar to an ulnar nerve subluxing over the medial epicondyle in an elbow during flexion.
The second type is what you have observed. The superior peroneal retinaculum is still intact and prevents the tendons from subliming up onto the malleolus, however the superior peroneal retinaculum is not normal. It has been injured and is now lax allowing the peroneal tendons to be hyper mobile beneath it. What you see in your case is what I also commonly observe with the peroneus brevis tendon snapping in underneath the peroneus longus tendon. It is really a transposition of the tendons.
Lovely work,
Steve